A metric for spatially explicit contributions to science-based species targets

Species threat abatement and restoration (STAR) metric

We developed and analysed a STAR metric that evaluates the potential benefit for threatened species of actions to reduce threats and restore habitat. Like the Red List Index^7,8, STAR is derived from existing data in the IUCN Red List and is intended to help address an urgent need. STAR is spatially explicit, enabling identification of specific threat abatement and habitat restoration opportunities in particular places, which, if implemented, could reduce species extinction risk to levels that would exist without ongoing human impact. Abatement of threats to species encompasses reduction in threat intensity and/or action to mitigate the impacts of threats. Positive population and/or distribution changes, along with the resulting reduction of species extinction risk, have been documented in response to threat abatement¹³. STAR assumes that, for the great majority of species (see Supplementary Discussion), complete alleviation of threats would reduce extinction risk through halting the decline and/or permitting sufficient recovery in population and distribution, such that the species could be downlisted to the IUCN Red List category of Least Concern. We recognize that complete threat reduction is difficult, incremental conservation gains will need to be tracked at the species level¹⁴ and species recovery will vary across a species’ range¹⁴.

For each species, a global STAR threat abatement (STAR_T) score is defined. This varies from zero for species of Least Concern to 100 for Near Threatened, 200 for Vulnerable, 300 for Endangered and 400 for Critically Endangered species (using established weighting ratios^7,8). The sum of STAR_T values across all species represents the global threat abatement effort needed for all species to become Least Concern. STAR_T scores can be disaggregated spatially, based on the area of habitat (AOH) currently available for each species in a particular location (as a proxy for population proportion). This shows the potential contribution of conservation actions in that location to reducing the extinction risk for all species globally. The local STAR_T score can be further disaggregated by threat, based on the known contribution of each threat to the species’ risk of extinction (see Methods). This quantifies how actions that abate a specific threat at a particular location contribute to the global abatement of extinction risk for all species.

The STAR metric also includes a complementary habitat restoration component to reflect the potential benefits to species of restoring lost habitat. During the United Nations Decade on Ecosystem Restoration (2021–2030), restoration efforts are likely to expand. The STAR restoration component applies a similar logic to the STAR threat abatement component, but for habitat that has been lost and is potentially restorable (that is, restorable AOH). The STAR restoration component does not make assumptions about the extent of habitat restoration required for individual species, but instead quantifies the potential contribution that habitat restoration activities could make to reducing species’ extinction risk. For a particular species at a particular location, the STAR restoration (STAR_R) score reflects the proportion that restorable habitat at the location represents of the global area of remaining habitat for that species. Importantly, a multiplier is applied to STAR_R scores to reflect the slower and lower success rate in delivering benefits to species from restored habitat compared with conserved existing habitat¹⁵. Again, STAR_R scores can be disaggregated by threat and summed across species within the location.

STAR is intended to provide a metric to underpin the establishment of science-based targets as explicit contributions from individual actors towards the post-2020 biodiversity framework, by allowing assessment of actions and locations according to their potential ability to deliver towards international conservation targets. Individual spatially based STAR_T and STAR_R scores, for all species present in a particular location or country, represent a proportion of the global opportunity to reduce species’ extinction risk through threat abatement and restoration, respectively. For each species, the total STAR_T score could be achieved by the complete abatement of all threats in remaining habitat, or an equivalent value of the STAR metric can be achieved by a combination of threat abatement in the remaining habitat and restoration of lost habitat (with concomitant threat abatement therein). The metric can support establishment of science-based targets by a range of actors across spatial scales. By enabling governments and non-state actors to quantify their potential contributions, STAR, along with other tools, could facilitate achievement of global policy goals, notably the species component of the Sustainable Development Goals and the expected post-2020 Global Biodiversity Framework.

STAR uses existing publicly available datasets: species’ extinction risk categories and threats available from the IUCN Red List⁶ (or, for country endemics not yet assessed globally, from national red lists); and species’ AOH estimated using species’ ranges, habitat associations, and elevation limits, along with digital elevation models and current and historical land cover maps (here, we used backcast land cover maps of the distribution of habitat pre-human impact, as in ref. ¹⁶). To demonstrate the utility of STAR, we calculated global STAR scores for the groups of terrestrial vertebrate species that are comprehensively assessed on the IUCN Red List (that is, threatened and Near Threatened species of amphibians, birds and mammals globally; n = 5,359).

Potential to reduce species extinction risk

Globally, the greatest contribution that could be made to reduce the extinction risk of these groups is tackling threats from annual and perennial non-timber crop production, which account for 24.5% of the global STAR_T score (Fig. 1). A further 16.4% is contributed by logging and wood harvesting. There are likely to be specific targets for reducing agriculture and forestry threats in the post-2020 framework³, and applying STAR quantifies the large potential contribution that mitigating these threats could make to the goal for species conservation. Appropriate activities to deliver on such targets range along a continuum from land sharing through to land sparing¹⁷.

STAR can be used in combination with existing policy and planning tools to quantify the potential contribution of action targets towards species conservation outcomes. The proposed post-2020 framework includes an action target for the protection of sites of particular importance to biodiversity³. Key Biodiversity Areas¹¹, which include Important Bird and Biodiversity Areas¹⁸ and Alliance for Zero Extinction sites¹⁹, correspond to such sites. Key Biodiversity Areas so far cover 8.8% of the terrestrial surface (www.keybiodiversityareas.org; identification is ongoing), but already capture 47% of the global STAR_T score for the vertebrate groups analysed. They represent large proportions of some national STAR_T scores: >70% in Mexico and Venezuela and >50% in Madagascar, Ecuador, the Philippines and Tanzania.

STAR_T scores can also support target setting at national and sub-national scales to help meet international policy goals. The control and eradication of invasive species forms one of the CBD’s proposed post-2020 action targets³. New Zealand has already set a Predator Free 2050 goal that aims to eradicate three invasive mammal species by 2050. New Zealand contributes 0.8% to the global STAR_T score for the three vertebrate groups included in this study. Achieving the Predator Free 2050 goal would contribute 30% of the total STAR_T score for New Zealand, amounting to 0.2% of the global STAR_T score.

All countries contribute towards the global STAR_T score, but scores are highly skewed, with a few countries having high STAR_T scores and most having low scores for the vertebrate groups analysed (Fig. 2a and Extended Data Fig. 1). The highest-scoring countries are located in biodiverse regions with many threatened endemic species²⁰: Indonesia contributes 7.1% of the global STAR_T score, Colombia 7.0%, Mexico 6.1%, Madagascar 6.0% and Brazil 5.2%. These top five countries contribute 31.3% of the global STAR_T score. In contrast, the lowest-scoring 88 countries together contribute only 1% of the global STAR_T score. This does not imply that these low-scoring countries have negligible species conservation responsibilities; the global decline in even common species indicates that all countries must act to reverse the degradation of nature and restore the diversity and abundance of species and integrity of ecosystems²¹, as well as preventing extinctions at a national scale. Moreover, most countries have a Red List Index²², or an equivalent, quantifying their progress or failure in reducing the global extinction risk of assessed species relative to their national responsibility for global species conservation. STAR provides a means to guide the reduction of extinction risk and so assist all countries in meeting national species conservation targets.

At the global level, we estimated that an equivalent to 55.9% of the global STAR_T score for vertebrates could, theoretically, be achieved by restoring lost habitat within the current range (Fig. 1). Ecosystem restoration objectives have been identified in many national biodiversity strategies for the CBD, as well as in many countries’ commitments under the Bonn Challenge, and as part of Nationally Determined Contributions under the United Nations Framework Convention on Climate Change. The STAR metric has the potential to support restoration initiatives alongside species conservation targets by quantifying the potential benefit to particular species of restoring habitat in specific places²³ (Fig. 2b). Restoration may be particularly important for some species, including those assessed under Red List sub-criteria D/D1 (with a very small population) or Bac (with a small range with severe fragmentation, plus extreme fluctuations). For species uniquely assessed under these criteria (2.8% of those included in this study), threat abatement alone is unlikely to eliminate extinction risk, so this might need to be complemented by restoration in order to achieve Least Concern status (see Supplementary Discussion). Moreover, depending on habitat loss and threat type, restoration of habitat may be beneficial for a larger proportion of threatened species.

Application of STAR at the landscape scale

We tested the landscape-scale application of the STAR metric in the southern part of Bukit Tigapuluh landscape, in central Sumatra, Indonesia (Fig. 3a). The Bukit Tigapuluh Sustainable Landscape and Livelihoods Project is a sustainable commercial rubber initiative. The study area (approximately 88,000 ha) includes a 5-km buffer (which is set aside to support local livelihoods, wildlife conservation areas and forest protection and restoration) and two ecosystem restoration areas (which form a conservation management zone that protects the Bukit Tigapuluh National Park from encroachment).

The total STAR_T score for the study area represents 0.2% of the STAR_T score for Sumatra, 0.04% of the STAR_T score for Indonesia and 0.003% of the global STAR_T. The major threats are from annual and perennial non-timber crops, logging and wood harvesting, and the collection of terrestrial animals (Fig. 3b). The proximate causes of these pressures in the project area are rubber cultivation, oil palm cultivation, industrial logging, subsistence wood cutting and hunting. STAR analysis shows that areas with the greatest potential to contribute to species conservation through threat mitigation are in remaining natural habitat close to the national park, with a small area of high potential also to the west, where the relatively small distribution of the orbiculus leaf-nosed bat (Hipposideros orbiculus) overlaps the site (Fig. 3a). Additionally, due to recent forest loss, 47% of the STAR_T score for the study area could be achieved through habitat restoration (that is, STAR_R). Investment in these management actions has the potential to deliver these quantified contributions to national and global biodiversity targets.

Operationalization and future development

The STAR metric makes use of the best available data, producing results that are relevant to policy and practice. However, there is scope for future refinement as the underlying data improve. Here, the STAR metric covers amphibians, birds and mammals globally, constituting a well-studied but small proportion of taxonomic diversity (see Extended Data Figs. 2 and 3 for variation among taxa). STAR can be expanded to other taxonomic groups, including freshwater and marine species, as data become available (reptiles, cacti, cycads, conifers, freshwater fish and reef-building corals are among the groups imminently available for incorporation). Global application of STAR will require comprehensive assessment of taxonomic groups, testing of the transferability of the STAR metric assumptions among taxa as Red List coverage expands, and further development of methods to calculate AOH. AOH calculation does not currently capture spatial variation in species’ population density, which will be important for many species¹⁴; such data have not been gathered on a global scale yet and could be incorporated as available.

The completeness of threat data in the IUCN Red List is uneven but is continually improving. The STAR metric does not currently reflect spatial variation in threat magnitude within species’ ranges; more broadly, there is a lack of information on the spatial distribution of threats²⁴. Most species included in this study have relatively small ranges; the total current AOH is <5,000 km² for 55%, <1,000 km² for 33% and within a single country for 66% (Extended Data Fig. 4). This prevalence of small ranges may reduce the significance of spatial variation in threats. Nevertheless, threats may vary spatially for any species not confined to a single location, and there is scope to use threat mapping to inform the likely spatial distribution of threats²⁴. Application of STAR at the landscape or site level, for instance, to set targets or identify management actions (for example, Fig. 3), will therefore require verification of the presence and distribution of threatened species (including restorable habitat) and assessment of the distribution and severity of threats. Such assessments should examine synergies among threats²⁵ and potential leakage in response to threat mitigation²⁶—context-specific processes that cannot be accounted for in the global metric. At the global level, periodic recalibration of STAR scores based on updated Red List assessments will be necessary to account for the emergence of new threats²⁷ and the changing extinction risk of species^7,8, as well as the inclusion of additional groups not previously assessed. Where uncertainty cannot be reduced in a given application of STAR, sensitivity analyses (for example, see Methods below and Extended Data Figs. 5–8) can be used to explore and quantify uncertainty. For a summary of sources of uncertainty and approaches to quantify and reduce uncertainty in STAR calculations, see Supplementary Table 1 and Extended Data Fig. 5.

STAR alone does not identify conservation priorities, but could be harnessed alongside other data (for example, on costs and benefits of conservation actions) to support conservation planning and prioritization¹². The STAR metric identifies what, in principle, needs to be done for species to achieve Least Concern status; however, the feasibility of abating threats will depend on the specific threat and context. Threats such as climate change or infectious disease cannot be reduced significantly through local action only. However, they may be mitigated through measures such as (for climate change) conservation translocations or increasing habitat connectivity to support distribution shifts²⁸. Habitat restoration is a particularly important strategy to mitigate climate change impacts, and STAR quantifies the contribution of habitat restoration in combination with threat abatement to reducing species’ extinction risk. Appropriate prioritization²³ and local planning are needed to identify the spatial urgency, feasibility and expected benefit from restoration. Furthermore, while in principle complete delivery of STAR_T would achieve downlisting to Least Concern for the great majority of species, the varying reasons for raised extinction risk reflected in different Red List criteria are, necessarily, not conveyed when creating a standardized index (see Supplementary Discussion). Moreover, delivery of STAR_T does not equate to long-term species recovery. Other tools exist to support more ambitious goals, notably the IUCN Green Status of Species, which is complementary to STAR in its data inputs and requirements, scope and audience, and in that it assesses progress towards species’ full recovery and ecological functionality¹⁰. Over time, the Green Status approach may also provide additional data that could enhance STAR, but the urgent need is to quantify how actions can contribute to achieving species goals using data that are already available.

Finally, countries with high STAR_T scores face intense pressures on biodiversity, but these pressures often originate from beyond their borders. This is owing to both global-scale threats, such as climate change and infectious disease, and market forces operating beyond national boundaries. Global-scale and transboundary threats cannot necessarily be addressed within habitats, but require concerted actions within and among countries (for example, through national commitments to reducing greenhouse gas emissions), implementation of biosecurity measures to prevent the spread of invasive alien species, and enforcement of restrictions imposed by the Convention on International Trade in Endangered Species of Wild Fauna and Flora. STAR scores can indicate the need for such actions, which then require implementation in a non-local context. International trade in commodities and services is an important and growing driver of biodiversity loss. Some countries with high consumption per capita (for example, in Northern Europe) have relatively low in-country STAR_T scores, suggesting that it is important to consider embodied (that is, full lifecycle) as well as direct impacts for products and processes. For example, Germany contributes only 0.01% of the global STAR_T score but is the third biggest importer of biodiversity impacts through commodity supply chains²⁹. There is therefore urgent need to advance supply chain analyses²⁹ in order to quantify and account for the biodiversity impacts driven by end consumers.

Policy implications

STAR can be disaggregated to identify and quantify the opportunities for both countries and non-state actors to contribute their shares of action towards a global species conservation goal. In doing so, STAR can support a framework analogous to the United Nations Framework Convention on Climate Change’s 2015 Paris Agreement, which provided a new model for global environmental governance. Uptake of this model among non-state actors has been promising, with 476 companies³⁰ and 98 cities³¹ (as of 5 October 2020) establishing science-based targets for greenhouse gas emissions reduction at the level necessary to deliver the Paris Agreement. Moreover, the approach will doubtless be applied to analyse whether the sum of Nationally Determined Commitments, set by individual countries, is indeed sufficient to hold climate change to 1.5–2 °C³². STAR provides an equivalent metric to guide the establishment of science-based targets for conserving species-level biodiversity. STAR will need to sit alongside equivalent metrics for ecosystems (for example, ref. ³³) and potentially also genetic diversity³⁴, consistent with the CBD’s definition of biological diversity, in supporting the establishment of science-based targets in the post-2020 framework.

The application of STAR would have important implications for conservation and sustainable development. In terms of the post-2020 biodiversity framework, it could facilitate the establishment of targets to mitigate threats to the level necessary to halt and reverse biodiversity loss. Such an approach could be extended across the other biodiversity-related conventions, with, for example, the Ramsar Convention on Wetlands calibrating its global target as the STAR_T score for wetland biodiversity. It could similarly be extended to inform delivery of the biodiversity-related targets of Sustainable Development Goals 14 (life below water) and 15 (life on land), aligned with the role of the Red List Index^7,8,9 as an official indicator. Finally, and perhaps most fundamentally, the approach provides a common metric for the conservation of threatened species that stands to incentivize voluntary contributions from actors beyond national governments: cities, states and provinces; the private sector; and indigenous and local communities. The increasing recognition of the importance of polycentric governance in addressing global environmental challenges³⁵ suggests that such broadening of contributions is not only desirable but essential and urgent.

Source: Ecology - nature.com